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Liquid crystals are characterized by the orientation of their molecules, the major axis of whose direction can be controlled by an applied electric or magnetic field. In the present paper the viscosity variation of three thermotropic liquid crystals in the nematic phase having different dielectric constants is studied at varying electric field strength, shear field strength and temperature. The results show that the viscosity of liquid crystals can be varied by the applied electric field strength and that a lower temperature reduces the threshold electric field strength for the electroviscous effect to appear as well as decreasing the attainable values at higher electric field strength. In addition, the frequency of the applied electric field has little effect on electroviscosity.